The present industrial standard high dose dosimeter is a plastic composite dosimeter comprising a mixture of a polymer and an organic dye of various compositions that has the property of absorbing optical photons (UV or visible) in proportion to the amount of ionizing radiation dose. The two primary commercial vendors are Far West (Goleta, Calif.) and Harwell (United Kingdom). While suitable to their purpose, these two manufacturer's products suffer from dose rate dependency, dependency of irradiation temperature during exposure, post-irradiation temperature effects, pre-concurrent-, and post irradiation humidity effects, light-induced response changes, and handling problems that make the dose determination a difficult process. The currently commercially available high dose dosimeters are analyzed by placing the polymer dosimeters within a spectrophotometer that measures optical absorption. One or more wavelengths are used to determine the ionizing radiation dose.
In addition, W. L. McLaughlin et. al. in their paper ELECTRON AND GAMMA-RAY DOSIMETRY USING RADIATION-INDUCED COLOR CENTERS IN LiF, Radiat. Phys. Chem. V 14. Pp. 467-480, 1979 describe a method for using single crystals of lithium fluoride as dosimeters. In this method, ionizing radiation creates F-centers in the lithium fluoride crystals. The amount of ionizing radiation received by large single crystals of lithium fluoride has been shown to be related to the absorption of light at a wavelength corresponding to the F-center absorption. In the case of lithium fluoride, the F-center absorption wavelength is in the ultraviolet range with a .lambda..sub.max of about 247 nm. While this method has minimal irradiation temperature and dose rate dependence, it relies on a single crystal. Despite efforts to make uniform single crystals, the single crystals reported by McLaughlin were not uniform in their optical absorption response to ionizing radiation and therefore would have to be individually calibrated. Further, alkali halide crystals such as LiF are soft and easily scratched. Once scratched, the crystal is useless for optical measurements. Finally, polished single crystals are far too costly at $10 to $100 each to be used for routine high dose dosimetry.
In addition, A. Waibel et. al. in their paper A METHOD OF INDIVIDUAL CALIBRATION OF LiF OPTICAL ABSORPTION DOSEMETERS, Radiation Protection Dosimetry V 47 Pp. 581-583, 1993 describe a method for using single crystals of lithium fluoride as dosimeters at high dose and high temperature. This work validated the use of F-center absorption in single lithium fluoride crystals as a method of dosimetry. Waibel also validated the large (20%) coefficient of variation between the response of different crystals of LiF to the same ionizing radiation dose.
In addition, optically stimulated luminescent dosimetry as taught by Miller in U.S. Pat. Nos. 5,272,348; 5,567,948 and 5,569,927 utilizes M-center re-emission of a photon of longer wavelength than the interrogating photon. This dosimetry is subject to dose rate dependence and temperature effects at high doses which lessens it utility as a routine dosimeter in commercial practice for high dose dosimetry at doses greater than 10 kiloGray.